The Tories are to launch the biggest crusade for personal morality since John Major's ill-fated 'back to basics' campaign, demanding the right for citizens to tackle teenage yobs physically and calling for a reduction in family breakdowns.

Dominic Grieve, the shadow Attorney General, told The Observer that people who slapped others or scuffled with youths while trying to stop crimes being committed should not be prosecuted. His words mark a clear break with David Cameron's 'hug a hoodie' rhetoric. Asked about family breakdowns, he said the strict Victorian approach to family life had, in some ways, been successful, adding that parents must be responsible for their children and communities.

'You can argue that our Victorian forebears succeeded in achieving something very unusual between the 1850s and 1900 in changing public attitudes by - dare one use the word - instilling moral codes. I don't want to suggest this was an ideal society, but it was one where a sense of moral values and of the responsibility people owed to each other did seem to be pervasive. There was a much greater sense of shame in respect of transgressions.'

His words come as former Tory leader Iain Duncan Smith prepares to publish a report on social justice tomorrow, blaming the breakdown of traditional families for poverty, school failure and crime. But rather than attack single mothers, he will blame men shirking their responsibilities. The report backs tax breaks for married couples, arguing the present tax credits system makes some couples better off apart.

The report by the Conservatives' social justice policy group, commissioned by Cameron, also questions why absent fathers are common in some communities: 57 per cent of Afro-Caribbean children are raised by lone parents, against 25 per cent of white children.

The new rhetoric revives a debate on personal responsibility not seen since the Major years, following criticism of Cameron's modernising agenda. It also challenges Labour ministers, who have toughened their stance on crime. A spokesman for John Reid, the Home Secretary, declined to comment on Grieve's views despite claims they could encourage vigilantes.

Grieve told The Observer that, decades ago, neighbours who forcibly tackled a young vandal would have been backed by the child's parents; now, individuals would be prosecuted for assault. People no longer expected support from either the police or passers-by for making a citizen's arrest: 'They take the view that if the matter gets out of control, there's a danger that if they lay hands on the young person they might be liable to prosecution for assault, even if their response is proportionate.

'The police must provide greater reassurance that they are not going to get mired in trivial allegations. If somebody is brought in to the police because they are committing vandalism and starts making trivial allegations that they were assaulted by the person who arrested them, this should be consigned to the dustbin unless there is evidence that real physical injury has been caused.'

The law did not allow hitting criminals outright, but they could be restrained during a citizens' arrest, he said, and if a struggle ensued people could use reasonable force. 'The niceties of what goes on cannot be subject to minute scrutiny, so if what is being complained about in terms of being assaulted is relatively trivial, it doesn't merit a great deal of considering, even if [the offender had been] slapped.'

Duncan Smith's report will say family breakdown costs £20bn a year, adding: 'At the heart of stable families and communities lies marriage. For too long this issue has been disparaged and ignored.' Underlining his traditional views, he told the Sunday Telegraph that gay couples were 'irrelevant' to family policy because only 0.5 per cent of Britons were gay. The true figure is six per cent.

His report says cohabiting parents are more likely to split than married couples, and warns of the risks of 'transient parenting', where children have a succession of short-term stepfathers.

It also backs more help for stay-at-home mothers, citing a YouGov poll showing nearly half of Britons think child-care subsidies paid to working mothers should also go to mothers at home.

The report may make difficult reading for two Tory MPs, James Gray and Greg Barker - both fathers who recently left their wives - but will trigger fresh debate about modern fatherhood.

John Hutton, the Work and Pensions Secretary, will publish plans this week forcing mothers to register the father's name on birth certificates, to make fathers recognise their responsibility. Fathers who do not pay child support will risk electronic tags and curfews.

Separately, ministers are considering scrapping requirements on IVF clinics to consider the baby's need for a father figure, making it easier for single women to become parents via fertility treatment.

The National Council for One Parent Families said the Tories should start tackling poverty within families of all types, adding: 'It is not lone parenthood itself that causes long-term poorer outcomes for children in one-parent families, but rather the poverty associated with lone parenthood and, where it exists, parental conflict before the separation.'